What's up ! It's often used as a greeting. It's meaning: -How are u ! -What's going on ! -What is new ! -How was you going! It's like Hi or What's new not like ask u How are u really , so we can't say I am fine or I'm well that is wrong ❌. We can say: Not much (not much new) Or Hi What's up!(back) Or What's up with you !